This invention relates to the vapor deposition of metal films and in particular to the thermally induced deposition of aluminum from volatile aluminum compounds and to an apparatus for effecting such deposition.
Many industrial processes, such as the fabrication of semiconductor devices or the construction of capacitors, require the deposition of metal films e.g. to provide electrodes or interconnecting conductor tracks.
Generally such metal films are provided by vacuum evaporation of the metal. This process however, requires very careful control to ensure that a hard vacuum is maintained and that traces of impurities are excluded. Furthermore, vacuum processing requires the provision of relatively expensive airlocks and involves considerable process time. To overcome these difficulties atmospheric pressure processes have been developed in which aluminum is thermally deposited by decomposition of a volatile aluminum compound, generally tri-isobutyl aluminum (TIBA). Such a process, however, has so far proved difficult to control and does not, in general, give reproducible results.
It is thought that many of the problems are caused by partial decomposition of TIBA prior to reaction and, in an attempt to prevent such decomposition, some workers have employed mixtures of TIBA and isobutylene. Such a technique, however, has been found to produce very poor results.